Abstract:

The Ocean Bottom Seismometer Augmentation to the Philippine Sea Experiment
(OBSAPS, April-May, 2011, R/V Revelle) addresses the coherence and depth dependence of
deep-water ambient noise and signals. During the 2004 NPAL Experiment in the North Pacific
Ocean, in addition to predicted ocean acoustic arrivals and deep shadow zone arrivals, we
observed "deep seafloor arrivals" that were dominant on the seafloor Ocean Bottom Seismometer
(OBS) (at about 5000m depth) but were absent or very weak on the Distributed Vertical Line
Array (DVLA) (above 4250m depth). These "deep seafloor arrivals" (DSFA) are a new class of
arrivals in ocean acoustics possibly associated with seafloor interface waves. The OBSAPS
cruise had three major research goals: a) identification and analysis of DSFAs occurring at short
(1/2CZ) ranges in the 50 to 400Hz band, b) analysis of deep sea ambient noise in the band 0.03
to 80Hz, and c) analysis of the frequency dependence of BR and SRBR paths as a function of
frequency. On OBSAPS we deployed a fifteen element VLA from 12 to 852m above the
seafloor, four short-period OBSs and two long-period OBSs and carried out an 11.5day
transmission program using a J15-3 acoustic source.